In general, an oriented film which uses a resin material such as polyethylene terephthalate, polypropylene and polyethylene, and is transparent and glossy has been widely used as a wrapping material. On the other hand, a matte film or sheet with controlled gloss, which has been conventionally used for a wall paper, a screen, an envelope, various files for a stationery, and the like, which dislike stray light, is supposed to be effective in enhancing an appeal and buying inclinations of a product in the packaging industry, and is demanded.
In relation to a matte film or sheet, for instance, Patent Document 1 (Japanese Patent No. 3172559) discloses a matte film for wall paper which is formed of an ethylene-vinyl alcohol copolymer containing 1 wt % or more of an inorganic filler, and has a gloss of 60% or less; Patent Document 2 (JP-A-2002-200724) discloses a matte biaxially-oriented polyester packaging film which includes 1 wt % or more of inactive particles such as organic or inorganic particles with a particular particle size, and has a gloss of 35% or less and an optical haze of 80% or less; and Patent Document 3 (Japanese Patent No. 3175306) discloses an annealed matte polypropylene film having a gloss of 30% or less and an optical haze of 18% or less.
However, when these resin materials are disposed, such a resin material as to have a low combustion heat quantity, be decomposed in soil and be safe has been expected from the viewpoint of environmental protection. A product using a biodegradable resin of aliphatic polyester such as a polylactic acid resin, specifically, a vessel such as a film/sheet and a bottle, a formed material, fiber, a nonwoven fabric, a foam and a composite material using them have been actively studied. However, the biodegradable film or sheet has not yet been obtained which is made from a polylactic acid resin and has excellent matte properties.
A polylactic acid resin is a polycondensate of lactic acid with an optically-active center, and has an optical purity (OP: in unit of %) calculated through the following equation on the basis of a composition ratio of monomer units of L-lactic acid and/or D-lactic acid constituting the polymer.OP=|[L]−[D]|, wherein [L]+[D]=100,(wherein [L] represents wt % for L-lactic acid constituting the polylactic acid resin; [D] represents wt % for D-lactic acid constituting the polylactic acid resin; and | | represents an absolute value of a calculated value).
The polylactic acid resin has such a property that the resin with a high optical purity of 80% or higher becomes crystalline and the resin with a low optical purity of lower than 80% becomes amorphous; has a lower optical haze (in accordance with ASTM-D1003-95) and more adequate transparency than the other biodegradable resins; has such excellent transparency, glossiness and rigidity as a gloss of 130% or more (in accordance with ASTM-D2457-70: at 45 degrees) and a tensile elasticity of about 2 to 5 GPa (in accordance with ASTM-D882-95a); but is brittle at room temperature (23° C.) and is inferior in matte properties, because of having the glass transition temperature Tg of about 60° C. which is especially higher than that of other biodegradable resins.
A polylactic acid resin has a defect of being inferior in impact resistance which is required when a packet is transported, because of having brittleness originally, so that an attempt has been conventionally made for the purpose of improving the impact resistance by mixing a biodegradable polyester which is superior in the impact resistance and has a low glass transition temperature Tg (10° C. or lower), with itself, but the attempt of improving matte properties has not been made. The term biodegradable polyester here means a crystalline resin which includes an aliphatic polyester obtained by polycondensing the main components containing aliphatic dicarboxylic acid and aliphatic diol, an aliphatic polyester obtained by ring-opening polymerizing cyclic lactone, a synthesized aliphatic polyester, and an aliphatic polyester biosynthesized in a bacterial cell; has a crystalline melting point in a range of 60 to 170° C. and a glass transition temperature of room temperature (23° C.) or lower; and is rubbery and has impact resistance at room temperature; but is inferior in transparency to that of the polylactic acid resin.
An oriented polylactic acid film or sheet made from a mixture mainly consisting of a polylactic acid resin and a biodegradable polyester with a glass transition temperature Tg of 0° C. or lower is disclosed in, for instance, Patent Document 4 (Japanese Patent No. 3138196) and the like, but any of them cannot be said to reach a practical level of matte properties, though having improved the impact resistance, and has a problem.
As for an oriented polylactic acid film or sheet mainly consisting of a mixture of a polylactic acid resin and inactive particles, Patent Document 5 (JP-A-2001-49003) discloses a method for obtaining the oriented polylactic acid film which contains 20 wt % of calcium carbonate having an average particle size of 0.6 μm, or 15 wt % of a polystyrene resin and 5 wt % of titanium oxide (in any of which the contents of inactive particles are 20 wt %), and is a white and opaque film. However, the film having excellent matte properties cannot be obtained only by merely adding the inorganic particles and the organic particles to a resin, and Patent Document 5 does not disclose the method of improving matte properties. Specifically, the film or sheet having adequate matte properties has not been obtained with the use of the polylactic acid resin.
Patent Document 6: (JP-A-8-502552), Patent Document 7 (Japanese Patent No. 2742892), Patent Document 8 (Japanese Patent No. 3008071), Patent Document 9 (Japanese Patent No. 3055001), Patent Document 10 (Japanese Patent No. 3154056) and Patent Document 11 (Japanese Patent No. 2939586) disclose a biodegradable film made from a chemically-modified-starch-based biodegradable resin which is a mixture consisting of mainly (50 wt % or more) at least one starch derivative selected from the group consisting of starch ester, starch ether and polyester graft polymer starch and a biodegradable polyester containing a polylactic acid resin, though they do not specifically disclose an oriented film made from a polylactic acid resin containing mainly (75 wt % or more) the polylactic acid resin. These documents disclose the film which is mainly made from the starch derivative having adequate compatibility with a biodegradable polyester including a polylactic acid polymer and is superior in transparency, but do not disclose the film having achieved adequate matte properties at all.
In addition, generally, when a resin of a main component is blended with a second resin having low compatibility with the main resin, the second resin is ununiformly mixed with the main resin, and the obtained blended substance becomes opaque. A film or sheet formed from the resin in such a blent state occasionally shows matte properties to some extent, but becomes fragile. It is often difficult to stably obtain the film or sheet from such a resin, and particularly to obtain a thin film.
Patent Document 1: Japanese Patent No. 3172559
Patent Document 2: JP-A-2002-200724
Patent Document 3: Japanese Patent No. 3175306
Patent Document 4: Japanese Patent No. 3138196
Patent Document 5: JP-A-2001-49003
Patent Document 6: JP-A-8-502552
Patent Document 7: Japanese Patent No. 2742892
Patent Document 8: Japanese Patent No. 3008071
Patent Document 9: Japanese Patent No. 3055001
Patent Document 10: Japanese Patent No. 3154056
Patent Document 11: Japanese Patent No. 2939586